An active matrix substrate is a main element of a display device. The active matrix substrate generally includes a display region and a periphery circuit region beside the display region, and is covered by an insulating layer. The insulating layer is used to protect a variety of electronic components of the active matrix substrate. A number of contact holes are generally defined in the insulating layer on the periphery circuit region to expose a number of conducting pads. The conducting pads are used to electrically connect the electronic components of the active matrix substrate to an external integrated circuit (IC) chip.
FIG. 1A is a schematic partial and top view of a chip connecting unit of a periphery circuit region of a conventional active matrix substrate. FIG. 1B is a schematic view of the chip connecting unit of FIG. 1A, showing a connection between a metal pad of the chip connecting unit and a bump of an IC chip. Referring to FIGS. 1A and 1B, a chip connecting unit 20 of a periphery circuit region of an active matrix substrate includes dozens or hundreds of conducting metal pads 22 (FIG. 1A shows only four metal pads 22). Each metal pad 22 is covered by a transparent conducting pad 25 and connected to a metal wire 23. The large number of the metal pads 22 is arranged in two rows for saving space. In addition, contact holes 24 are defined, and each of the contact holes 24 corresponds to one of the metal pads 22. A dimension of each of the contact holes 24 is less than that of the corresponding metal pad 22. With this configuration, a portion of the metal pad 22 and the transparent conducting layer 25 formed on the metal pad 22 is exposed by the contact hole 24. In a bonding process for connecting an active matrix substrate having the contact hole 24 with an IC chip, conductive particles 30 of an anisotropic conductive adhesive are generally provided to electrically connect the metal pads 22 to bumps 27 of the IC chip 26.
However, in conventional technology, an insulating layer 28 is provided at a region below the IC chip 26 except the bonding regions for the bumps 27. The insulating layer 28 generally contains resin, so the insulating layer 28 tends to expand when absorbing water vapor. This may result in an electrical disconnection between the bumps 27 of the IC chip 26 and the metal pads 22 of the chip connecting unit 20 of the periphery circuit region. Thus, reliability of the display device is easy to be lowered, which may result in display abnormal.
FIG. 2A is a schematic partial and top view of a chip connecting unit of a periphery circuit region of another conventional active matrix substrate. FIG. 2B is a schematic view of the chip connecting unit of FIG. 2A, showing a connection between a metal pad of the chip connecting unit and a bump of an IC chip. Referring to FIGS. 2A and 2B, each chip connecting unit 20a defines only one contact hole 24a. The contact hole 24a is used to expose all the metal pads 22 of the chip connecting unit 20a. In a bonding process for connecting an active matrix substrate having the contact hole 24a with an IC chip, the electrical disconnection caused by expansion of the resin when absorbing water vapor can be avoided. However, as an insulating layer below the bump 27 of the IC chip 26 is entirely omitted, a short circuit may be formed between the metal pad 22 and a metal wire 23 adjacent to the metal pad 22. More specifically, the short circuit is caused by an electrical connection of the bump 27 of the IC chip 26 and the metal wire 23 adjacent to the bump 27 via the conductive particles 30 of the anisotropic conductive adhesive when the IC chip 26 is not accurately aligned in the bonding process. Accordingly, production yield of the display device is reduced.